1. Field of the Invention
The present invention relates to a method for the manufacture of large area silicon crystal bodies for solar cells, utilizing silicon powder of a small crystal grain size as the starting material, and converting the same into the form of a foil by means of a sintering process.
2. Description of the Prior Art
A method similar to the one described is known from German OS No. 29 27 086 (U.S. Pat. No. 4,330,358). In this method, a silicon foil is produced by combining a silicon powder with an organic binder to form a slip and the slip is drawn out onto a substrate. The slip is sintered in an argon gas atmosphere at 1350.degree. C., whereby the silicon grains of less than 1 micron diameter grow to grains having a diameter greater than the foil thickness. The sintering temperature is selected so as to be as close as possible to the melting temperature and the sintering is continued until an adequate grain growth has occurred.
The grain growth and the shrinkage, however, are greatly impeded by the oxide skin which surrounds each silicon grain. A satisfactory shrinkage can only occur where a melting process has occurred. In a long-term sintering, melting must be avoided because of the reaction with the substrate.
German OS No. 30 17 923A 1 discloses a method for the manufacture of a silicon foil in which, during the sintering process, the silicon foil is briefly melted at its surface region with one or more heat pulses. The heat is generated by means of a hot air stream and the non-melted underside of the sintered silicon foil is removed. This method is relatively complicated and, due to the removal of the back side of the film, is not well suited for the manufacture of economical solar cell base materials because of the material loss and because of the reduced yield resulting therefrom. Moreover, a continuous fabrication process based on this technique is difficult to implement.